FastAPI version 0.119.0 introduced partial support for Pydantic v1 from inside of Pydantic v2 (as `pydantic.v1`), to facilitate the migration to v2.

FastAPI 0.126.0 dropped support for Pydantic v1, while still supporting `pydantic.v1` for a little while.

/// warning

The Pydantic team stopped support for Pydantic v1 for the latest versions of Python, starting with **Python 3.14**.

  }

  @Override
  public int read() throws IOException {
    while (in != null) {
      int result = in.read();
      if (result != -1) {
        return result;
      }
      advance();
    }
    return -1;
  }

  @Override
  public int read(byte[] b, int off, int len) throws IOException {
    checkNotNull(b);
    while (in != null) {
      int result = in.read(b, off, len);
      if (result != -1) {

  private static final class Failure {
    static final Failure FALLBACK_INSTANCE =
        new Failure(
            new Throwable("Failure occurred while trying to finish a future.") {
              @Override
              public Throwable fillInStackTrace() {
                return this; // no stack trace
              }
            });
    final Throwable exception;

    }

    @Override
    protected @Nullable EndpointPair<N> computeNext() {
      while (true) {
        /*
         * requireNonNull is safe because visitedNodes isn't cleared until this method calls
         * endOfData() (after which this method is never called again).
         */
        requireNonNull(visitedNodes);
        while (successorIterator.hasNext()) {
          N otherNode = successorIterator.next();

      return 2;
    }
    // Correct the size for open addressing to match desired load factor.
    // Round up to the next highest power of 2.
    int tableSize = Integer.highestOneBit(setSize - 1) << 1;
    while (tableSize * DESIRED_LOAD_FACTOR < setSize) {
      tableSize <<= 1;
    }
    return tableSize;
  }

  static CharMatcher from(BitSet chars, String description) {
    // Compute the filter.
    long filter = 0;

   */
  static BigInteger randomPositiveBigInteger(int numBits) {
    BigInteger result;
    do {
      result = randomNonNegativeBigInteger(numBits);
    } while (result.signum() == 0);
    return result;
  }

  /**
   * Generates a number in [0, 2^numBits) with an exponential distribution. The floor of the log2 of

                        res = r.combine(next);
                    } else {
                        res.append(r.combine(next));
                    }
                } while (next != nextstart);
            }
        } while (r != start);

        if (res != null) {
            return res;
        }

        return dr;
    }

    /**
     * @param domains
     */

    public static void setText(Element element, String value) {
        while (element.hasChildNodes()) {
            element.removeChild(element.getFirstChild())
        }
        element.appendChild(element.ownerDocument.createTextNode(value))
    }

    public static void setChildren(Node element, Closure cl) {
        while (element.hasChildNodes()) {
            element.removeChild(element.getFirstChild())
        }

      if (swallowIOException) {
        logger.log(Level.WARNING, "IOException thrown while closing Closeable.", e);
      } else {
        throw e;
      }
    }
  }

  /**
   * Closes the given {@link InputStream}, logging any {@code IOException} that's thrown rather than
   * propagating it.
   *
   * <p>While it's not safe in the general case to ignore exceptions that are thrown when closing an

                }
            } while (++si % 16 != 0);
            c[ci++] = ' ';
            c[ci++] = ' ';
            c[ci++] = '|';
            System.arraycopy(d, 0, c, ci, 16);
            ci += 16;
            c[ci++] = '|';
            NL.getChars(0, NL_LENGTH, c, ci);
            ci += NL_LENGTH;
        } while (si < length);

        ps.println(c);
    }

    /**