NXC Nuveen California Select Tax Free Income Portfolio

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Table of Contents

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 Chair’s Letter
to Shareholders

Dear Shareholders,

In February, the world witnessed Russia invade Ukraine. We are now almost two months into the conflict and are beginning to see the scale of the humanitarian crisis and the economic impact caused by this event.

Given the fluidity of the situation, market uncertainty is currently elevated. Economic conditions were already challenging prior to the invasion, with inflation lingering at multi-decade highs, interest rates expected to continue rising, economic growth moderating from the post-pandemic recovery, and weakening performance across equity markets and some bond market segments. The Russia-Ukraine conflict has accelerated these trends in the short term. The spike in geopolitical risks led to surging prices for oil and other hard and soft commodities, driving both inflation and recession risks higher. The U.S. Federal Reserve (Fed) and other central banks now face an even more difficult task of slowing inflation without pulling the economy into recession. As anticipated, the Fed began the rate hiking cycle in March 2022, raising its short-term rate by 0.25% from near zero for the first time since the pandemic was declared two years ago and now signaling rate increases of 0.5% in the near future. Where the Russia-Ukraine conflict goes from here, how inflation impacts economic growth and the Fed’s response to changing economic conditions are difficult to forecast.

In the meantime, while markets will likely continue fluctuating with the daily headlines, we encourage investors to keep a long-term perspective. To learn more about how well your portfolio is aligned to your time horizon, risk tolerance and investment goals, consider reviewing it with your financial professional.

On behalf of the other members of the Nuveen Fund Board, I look forward to continuing to earn your trust in the months and years ahead.

Terence J. Toth
Chair of the Board
April 21, 2022

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Important Notices

For Shareholders of Nuveen California Municipal Value Fund (NCA)

Fund Reorganization

Effective prior to the opening of business on March 8, 2021, Nuveen California Municipal Value Fund 2 (NCB) was reorganized into NCA (the “Reorganizations”). Refer to Note 1 and Note 10 of the Notes to Financial Statements within this report for further details on the Reorganization.

For Shareholders of Nuveen California Select Tax-Free Income Portfolio (NXC)

Change in Fiscal and Tax Year End

Effective February 24, 2022, NXC’s fiscal and tax year end changed from March 31 to February 28/29 as approved by the Fund’s Board of Trustees. As a result, NXC has prepared an annual report for the period April 1, 2021 through February 28, 2022 (the “eleven months ended February 28, 2022”).

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Portfolio Manager’s Comments

Nuveen California Quality Municipal Income Fund (NAC)

Nuveen California ATM-Free Quality Municipal Income Fund (NKX)

Nuveen California Municipal Value Fund (NCA)

Nuveen California Select Tax-Free Income Portfolio (NXC)

These Funds feature portfolio management by Nuveen Asset Management, LLC (NAM), an affiliate of Nuveen Fund Advisors, LLC, the Funds’ investment adviser. Portfolio manager Scott R. Romans, PhD, reviews U.S. economic and market conditions, key investment strategies and the twelve-month performance of these Nuveen California Municipal Funds.

For more information on the Funds’ investment objectives and policies, please refer to the Shareholder Update section at the end of the report.

What factors affected the U.S. economy and municipal bond markets during the twelve-month reporting period ended February 28, 2022?

The U.S. economic recovery remained on course over the twelve-month reporting period, despite setbacks from the COVID-19 virus, higher-than-expected inflation readings and increasing geopolitical tensions in Eastern Europe. Since the pandemic reached the U.S. in early 2020, the federal government has enacted $5.3 trillion in crisis-related aid and the U.S. Federal Reserve (Fed) kept borrowing rates low for businesses and individuals and kept the credit system stable while the jobs market and economy recovered from the pandemic shock. These measures, along with increasing vaccinations and improved treatments, helped the economy to reopen and activity to rebound during 2021, despite additional COVID-19 surges caused by new, more contagious variants. U.S. gross domestic product (GDP) rose at an annualized 6.9% in the fourth quarter of 2021, accelerating from 2.3% in the third quarter when the delta variant weighed on economic activity, according to the Bureau of Economic Analysis third estimate. Also according to the third estimate, GDP grew 5.7% in 2021 overall, rebounding from the contraction of -3.4% in 2020.

The return of consumer demand put upward pressure on inflation. However, as supply chains remained under stress and labor shortages continued, in part because of COVID-19 resurgences around the world, inflation appeared to be more durable than initially expected. The Fed responded by reducing its pandemic-era support programs and signaled that rate increases were likely in 2022 (which did materialize in March 2022, after the close of this reporting period, with a 0.25% increase in the Fed’s target interest rate). Interest rate and stock price volatility increased as markets considered whether the Fed could cool inflation without pulling the economy into recession. While some pandemic-related risks appeared to be receding, Russia’s invasion of Ukraine in late February 2022 brought forth another large-scale human tragedy with significant economic consequences. Inflation pressures rose

This material is not intended to be a recommendation or investment advice, does not constitute a solicitation to buy, sell or hold a security or an investment strategy and is not provided in a fiduciary capacity. The information provided does not take into account the specific objectives or circumstances of any particular investor, or suggest any specific course of action. Investment decisions should be made based on an investor’s objectives and circumstances and in consultation with his or her advisors.

Certain statements in this report are forward-looking statements. Discussions of specific investments are for illustration only and are not intended as recommendations of individual investments. The forward-looking statements and other views expressed herein are those of the portfolio manager as of the date of this report. Actual future results or occurrences may differ significantly from those anticipated in any forward-looking statements, and the views expressed herein are subject to change at any time, due to numerous market and other factors. The Funds disclaim any obligation to update publicly or revise any forward-looking statements or views expressed herein.

For financial reporting purposes, the ratings disclosed are the highest rating given by one of the following national rating agencies: Standard & Poor’s Group (S&P), Moody’s Investors Service, Inc. (Moody’s) or Fitch, Inc. (Fitch). This treatment of split-rated securities may differ from that used for other purposes, such as for Fund investment policies. Credit ratings are subject to change. AAA, AA, A and BBB are investment grade ratings, while BB, B, CCC, CC, C and D are below investment grade ratings. Holdings designated N/R are not rated by these national rating agencies.

Bond insurance guarantees only the payment of principal and interest on the bond when due, and not the value of the bonds themselves, which will fluctuate with the bond market and the financial success of the issuer and the insurer. Insurance relates specifically to the bonds in the portfolio and not to the share prices of a Fund. No representation is made as to the insurers’ ability to meet their commitments.

Refer to the Glossary of Terms Used in this Report for further definition of the terms used within this section.

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further on anticipated supply disruptions in energy, metals and grains, downside risks to global economic growth increased, and economic sanctions from Western countries sought to block Russia’s access to the global financial system. A more uncertain inflation and economic outlook also made the path toward monetary policy normalization more uncertain for the Fed and other central banks, contributing to elevated market volatility toward the end of the reporting period.

The broad municipal market declined slightly over the twelve-month reporting period. Municipal yields rose but not uniformly across the maturity spectrum, resulting in a flatter yield curve overall but with intermediate maturities outperforming the short and long ends of the curve. Demand for municipal debt remained remarkably strong throughout 2021, but outflows followed in early 2022 as dealers reduced their inventories in the higher volatility environment. Nevertheless, credit spreads were generally stable as municipal fundamentals were strong and the municipal market remained relatively insulated from geopolitical concerns abroad.

What were the economic and market environments in California during the twelve-month reporting period ended February 28, 2022?

California’s $3.1 trillion economy is the largest in the United States and has continued its post-pandemic recovery. The state’s unemployment rate was 5.4% as of February 2022, higher than the nation’s 3.8% rate. According to the S&P CoreLogic Case-Shiller Index, home prices in San Diego, Los Angeles and San Francisco rose 25.9%, 19.3% and 18.8%, respectively, over the twelve months ended December 2021 (the most recent data available at the time this report was prepared), compared with an average increase of 18.8% nationally. The Fiscal Year 2022 (July 1, 2021 to June 30, 2022) general fund budget for the state totals $196.4 billion, which is 18.3% higher than the revised Fiscal Year 2021 budget. The Fiscal Year 2022 budget projected a $47 billion surplus driven by revenues that were significantly higher and state costs that were lower than initially expected. The proposed Fiscal Year 2022-2023 (July 1, 2022 to June 30, 2023) budget of $213.1 billion represents a 1.5% increase over the revised Fiscal Year 2022 budget and projects a $45.7 billion surplus, of which 86% is expected to be allocated to one-time spending: health care, homelessness, housing, schools, COVID-19 and climate change. As of March 2022, Standard & Poor’s (S&P) affirmed its AA- rating on California general obligation (GO) debt, but S&P changed the outlook from stable to positive based on “the state’s projection of a new long-term structural balance and high reserves, even assuming currently high capital gains tax and federal aid revert to historically lower levels in later years.” Moody’s Investors Service affirmed its state GO rating of Aa2 with a stable outlook. California municipal bond supply totaled $79.1 billion for the twelve-month period ended February 28, 2022, a 6.4% increase from the same period a year earlier.

What key strategies were used to manage the Funds during the twelve-month reporting period ended February 28, 2022?

Each Fund seeks to provide current income exempt from both regular federal and California state income taxes, and in the case of NKX the alternative minimum tax (“AMT”) applicable to individuals, by investing primarily in a portfolio of municipal obligations issued by state and local government authorities within the state of California or certain U.S. territories. To the extent that the Funds invest in bonds of municipal issuers located in other states, each Fund may have income that is not exempt from state personal income tax. NCA’s use of tender option bonds to more efficiently implement its investment strategy may create up to 10% effective leverage (although the Fund had no such leverage at the end of the reporting period).

The rising interest rate environment in this reporting period provided an opportunity for the municipal investment team to buy lower rated, higher yielding credits in the Funds at wider credit spreads and with incrementally higher yields. These new purchases were funded by selling higher grade, lower yielding paper that had been bought when prevailing interest rates were lower, for the purposes of keeping the Funds fully invested and holding a more liquid investment that could be sold when longer-term opportunities arise. The Funds also used the proceeds from called and maturing bonds to buy new bonds. As a result, the Funds’ holdings in BBB, BB and B rated bonds increased, while exposures to AAA, AA and A rated bonds decreased over this reporting period. Additionally, as interest rates rose in the early months of 2022, the Funds sold some lower book yield positions at a loss to reinvest in more attractive, higher book yield opportunities. The investment team implemented this approach to enhance the Funds’ income earning capability and seek to make the Funds more tax efficient.

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From a sector standpoint, positioning remained relatively stable overall. The more noticeable changes included an increase in multi-family housing holdings, specifically in workforce housing - a new program that finances affordable housing for moderate/middle income families. The workforce housing sector was an area of significant new issuance in the California tax-exempt market during the reporting period and the Funds participated in several of these deals. The Funds saw a decrease in tobacco exposure, driven by refundings and restructurings in the sector, as well as declines in utilities and tax supported debt allocations, in which the Funds sold some of the placeholder bonds to rotate into higher yielding, lower rated credits. Elevated refunding activity during the reporting period resulted in a “passive” increase in the Funds’ allocations to pre-refunded bonds.

How did the Funds perform during the twelve-month reporting period ended February 28, 2022, and for NXC the eleven-month abbreviated reporting period ended February 28, 2022?

For the twelve months ended February 28, 2022, the Nuveen California Municipal Value Fund (NCA) outperformed the S&P Municipal Bond California Index, while Nuveen California Quality Municipal Income Fund (NAC) and Nuveen California ATM-Free Quality Municipal Income Fund (NKX) underperformed the S&P Municipal Bond California Index. For the eleven months ended February 28, 2022, the Nuveen California Select Tax-Free Income Portfolio (NXC) performed in-line with the S&P Municipal Bond California Index. For the purposes of this Performance Commentary, references to relative performance are in comparison to the S&P Municipal Bond California Index.

The main factors that contributed positively to the Funds’ relative performance were individual security selection, credit ratings allocations and sector allocations (except in NXC where sector allocation was a detractor from relative performance). In particular, the Funds’ overweight allocations to lower rated credits and sectors added the most to relative performance, especially in BBB rated and below investment-grade rated bonds, which outperformed during the reporting period.

Offsetting these positive relative performance factors were duration and yield curve positioning, including whether or not the Funds used leverage. The Funds’ longer duration positioning detracted from relative performance as longer duration bonds underper-formed the market during the reporting period. The Funds continued to emphasize longer duration (12 years and longer) bonds because their incrementally higher yields help support the Funds’ income earnings capability and have contributed to the Funds’ total returns over the long term. Additionally, NAC’s and NKX’s use of leverage, as part of the Funds’ duration management strategy, also weighed on relative performance versus the benchmark and was the main reason for the two Funds’ relative underperformance. In contrast, NCA and NXC do not use leverage and performed in-line or better versus the benchmark during the reporting period. Leverage is discussed in more detail later in the Fund Leverage section of this report.

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Fund Leverage

IMPACT OF THE FUNDS’ LEVERAGE STRATEGIES ON PERFORMANCE

One important factor impacting the returns of the Funds’ common shares relative to their comparative benchmarks was the Funds’ use of leverage through their issuance of preferred shares and/or investments in inverse floating rate securities, which represent leveraged investments in underlying bonds. The Funds use leverage because our research has shown that, over time, leveraging provides opportunities for additional income. The opportunity arises when short-term rates that the Fund pays on its leveraging instruments are lower than the interest the Fund earns on its portfolio of long-term bonds that it has bought with the proceeds of that leverage. This has been particularly true in the recent market environment where short-term rates have been low by historical standards.

However, use of leverage can expose Fund common shares to additional price volatility. When a Fund uses leverage, the Fund’s common shares will experience a greater increase in their net asset value if the municipal bonds acquired through the use of leverage increase in value, but will also experience a correspondingly larger decline in their net asset value if the bonds acquired through leverage decline in value. All this will make the shares’ total return performance more variable, over time.

In addition, common share income in levered funds will typically decrease in comparison to unlevered funds when short-term interest rates increase and increase when short-term interest rates decrease. In recent quarters, fund leverage expenses have generally tracked the overall movement of short-term tax-exempt interest rates. While fund leverage expenses are somewhat higher than their recent lows, leverage nevertheless continues to provide the opportunity for incremental common share income, particularly over longer-term periods.

Leverage from issuance of preferred shares and the use of leverage through inverse floating rate securities had a negative impact on the performance of NAC and NKX over the reporting period. NCA and NXC did not utilize leverage over the reporting period.

As of February 28, 2022, the Funds’ percentages of leverage are as shown in the accompanying table.

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Refer to Notes to Financial Statements, Note 5 — Fund Shares, for further details on preferred shares and each Fund’s respective transactions.

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Each Fund seeks to pay regular monthly dividends out of its net investment income at a rate that reflects its past and projected net income performance. To permit each Fund to maintain a more stable monthly dividend, the Fund may pay dividends at a rate that may be more or less than the amount of net income actually earned by the Fund during the period. Distributions to common shareholders are determined on a tax basis, which may differ from amounts recorded in the accounting records. In instances where the monthly dividend exceeds the earned net investment income, the Fund would report a negative undistributed net ordinary income. Refer to Note 6 – Income Tax Information for additional information regarding the amounts of undistributed net ordinary income and undistributed net long-term capital gains and the character of the actual distributions paid by the Fund during the period.

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Common Share Information (continued)

All monthly dividends paid by each Fund during the current reporting period were paid from net investment income. If a portion of the Fund’s monthly distributions is sourced or comprised of elements other than net investment income, including capital gains and/or a return of capital, shareholders will be notified of those sources. For financial reporting purposes, the per share amounts of each Fund’s distributions for the reporting period are presented in this report’s Financial Highlights. For income tax purposes, distribution information for each Fund as of its most recent tax year end is presented in Note 6 – Income Tax Information within the Notes to Financial Statements of this report.

NUVEEN CLOSED-END FUND DISTRIBUTION AMOUNTS

The Nuveen Closed-End Funds’ monthly and quarterly periodic distributions to shareholders are posted on www.nuveen.com and can be found on Nuveen’s enhanced closed-end fund resource page, which is at https://www.nuveen.com/resource-center-closed-end-funds, along with other Nuveen closed-end fund product updates. To ensure timely access to the latest information, shareholders may use a subscribe function, which can be activated at this web page (https://www.nuveen.com/subscriptions).

COMMON SHARE EQUITY SHELF PROGRAM

During the current reporting period, NKX was authorized by the Securities and Exchange Commission to issue additional common shares through an equity shelf program (“Shelf Offering”). Under this program NKX, subject to market conditions, may raise additional capital from time to time in varying amounts and offering methods at a net price at or above the Fund’s NAV per common share. Under the Shelf Offering, NKX was authorized to issue additional shares as shown in the accompanying table.

* Represents additional authorized common shares for the period March 1, 2021 through June 30, 2021.

During the current reporting period, NKX did not sell common shares through its shelf program.

Refer to the Notes to Financial Statements, Note 5 – Fund Shares for further details of Shelf Offering and the Fund’s transactions.

COMMON SHARE REPURCHASES

During August 2021, the Funds’ Board of Trustees reauthorized an open–market share repurchase program, allowing each Fund to repurchase an aggregate of up to approximately 10% of its outstanding common shares.

During the current reporting period, the Funds did not repurchase any of their outstanding common shares. As of February 28, 2022, (and since the inception of the Funds’ repurchase programs), each Fund has cumulatively repurchased and retired its outstanding common shares as shown in the accompanying table.

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Refer to the Glossary of Terms Used in this Report for further definition of the terms used within this section.