@@ -28,6 +28,11 @@ bazel_dep(name = "rules_android", version = "0.7.3")
 bazel_dep(name = "rules_shell", version = "0.8.0")
 bazel_dep(name = "googleapis-java", version = "1.1.5")
 bazel_dep(name = "cel-spec", version = "0.25.3", repo_name = "cel_spec")
+git_override(
+    module_name = "cel-spec",
+    commit = "21ec6f4e52e8d694687ff9ed7408d3eccbb955d7",
+    remote = "https://github.com/cel-expr/cel-spec",
+)
 bazel_dep(name = "rules_go", version = "0.65.0")
 
 # Required by cel-spec to satisfy gazelle transitive dependency
@@ -102,7 +107,6 @@ maven.install(
         "org.jline:jline-reader:" + JLINE_VERSION,
         "org.jline:jline-terminal:" + JLINE_VERSION,
         "org.jspecify:jspecify:1.0.1",
-        "org.threeten:threeten-extra:1.11.0",
         "org.yaml:snakeyaml:2.7",
         "tools.aqua:z3-turnkey:4.14.1",
     ],
 
@@ -520,12 +520,10 @@ public abstract static class Builder {
     public abstract Builder enableJsonFieldNames(boolean value);
 
     /**
-     * Enable or disable validating that duration values resulting from timestamp arithmetic do not
-     * overflow 64-bit nanoseconds. Defaults to enabled.
-     *
-     * <p>Disabling this option is an out-of-conformance behavior that suppresses nanosecond
-     * overflow validation when subtracting timestamps.
+     * @deprecated No-op. CEL durations now support the full protobuf duration range, so subtracting
+     *     valid timestamps never overflows.
      */
+    @Deprecated
     public abstract Builder enableTimestampOverflowCheck(boolean value);
 
     /**
 
@@ -426,7 +426,6 @@ cel_android_library(
     deps = [
         "//common/annotations",
         "@maven//:com_google_errorprone_error_prone_annotations",
-        "@maven//:com_google_guava_guava",
         "@maven_android//:com_google_guava_guava",
         "@maven_android//:com_google_protobuf_protobuf_javalite",
     ],
@@ -438,8 +437,10 @@ java_library(
     tags = [
     ],
     deps = [
+        ":proto_time_utils",
         "//common/annotations",
         "//common/exceptions:bad_format",
+        "@maven//:com_google_errorprone_error_prone_annotations",
         "@maven//:com_google_guava_guava",
         "@maven//:com_google_protobuf_protobuf_java",
     ],
@@ -451,8 +452,10 @@ cel_android_library(
     tags = [
     ],
     deps = [
+        ":proto_time_utils_android",
         "//common/annotations",
         "//common/exceptions:bad_format",
+        "@maven//:com_google_errorprone_error_prone_annotations",
         "@maven_android//:com_google_guava_guava",
         "@maven_android//:com_google_protobuf_protobuf_javalite",
     ],
 
@@ -14,7 +14,15 @@
 
 package dev.cel.common.internal;
 
+import static dev.cel.common.internal.ProtoTimeUtils.DURATION_SECONDS_MAX;
+import static dev.cel.common.internal.ProtoTimeUtils.DURATION_SECONDS_MIN;
+import static dev.cel.common.internal.ProtoTimeUtils.MAX_NANOS;
+import static dev.cel.common.internal.ProtoTimeUtils.NANOS_PER_SECOND;
+import static dev.cel.common.internal.ProtoTimeUtils.TIMESTAMP_SECONDS_MAX;
+import static dev.cel.common.internal.ProtoTimeUtils.TIMESTAMP_SECONDS_MIN;
+
 import com.google.common.base.Strings;
+import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.protobuf.Timestamp;
 import dev.cel.common.annotations.Internal;
 import dev.cel.common.exceptions.CelBadFormatException;
@@ -32,14 +40,8 @@
 public final class DateTimeHelpers {
   public static final String UTC = "UTC";
 
-  // Timestamp for "0001-01-01T00:00:00Z"
-  private static final long TIMESTAMP_SECONDS_MIN = -62135596800L;
-  // Timestamp for "9999-12-31T23:59:59Z"
-  private static final long TIMESTAMP_SECONDS_MAX = 253402300799L;
-
-  private static final long DURATION_SECONDS_MIN = -315576000000L;
-  private static final long DURATION_SECONDS_MAX = 315576000000L;
-  private static final int NANOS_PER_SECOND = 1000000000;
+  private static final Duration DURATION_MIN = Duration.ofSeconds(DURATION_SECONDS_MIN, -MAX_NANOS);
+  private static final Duration DURATION_MAX = Duration.ofSeconds(DURATION_SECONDS_MAX, MAX_NANOS);
 
   /**
    * Constructs a new {@link LocalDateTime} instance
@@ -79,6 +81,14 @@ public static LocalDateTime newLocalDateTime(Instant instant, String tz) {
     return instant.atZone(timeZone(tz)).toLocalDateTime();
   }
 
+  /** Creates an {@link Instant} from epoch seconds, validating CEL timestamp bounds. */
+  // CEL's timestamp(int) conversion accepts epoch seconds as an int64.
+  @SuppressWarnings("GoodTime-ApiWithNumericTimeUnit")
+  public static Instant fromSecondsToInstant(long seconds) {
+    checkSecondsValid(seconds);
+    return Instant.ofEpochSecond(seconds);
+  }
+
   /**
    * Parse from RFC 3339 date string to {@link java.time.Instant}.
    *
@@ -92,6 +102,75 @@ public static Instant parse(String text) {
     return instant;
   }
 
+  /** Parses a CEL duration string (following Go {@code time.ParseDuration} syntax). */
+  public static Duration parseDuration(String text) {
+    if (text.isEmpty()) {
+      throw invalidDurationFormat();
+    }
+    int len = text.length();
+    int i = 0;
+    char first = text.charAt(0);
+    boolean negative = (first == '-');
+    if (negative || first == '+') {
+      i++;
+    }
+    if (i == len) {
+      throw invalidDurationFormat();
+    }
+    if (len - i == 1 && text.charAt(i) == '0') {
+      return Duration.ZERO;
+    }
+    long totalSeconds = 0;
+    long totalNanos = 0;
+    while (i < len) {
+      int intStart = i;
+      int intEnd = scanAsciiDigits(text, intStart);
+      int fracStart = intEnd;
+      int fracEnd = intEnd;
+      if (intEnd < len && text.charAt(intEnd) == '.') {
+        fracStart = intEnd + 1;
+        fracEnd = scanAsciiDigits(text, fracStart);
+      }
+      if (intStart == intEnd && fracStart == fracEnd) {
+        throw invalidDurationFormat();
+      }
+      i = fracEnd;
+      int unitStart = i;
+      while (i < len && text.charAt(i) != '.' && !isAsciiDigit(text.charAt(i))) {
+        i++;
+      }
+      long unitNanos = parseUnitNanos(text, unitStart, i);
+
+      long segSeconds = 0;
+      long segNanos = 0;
+      for (int p = intStart; p < intEnd; p++) {
+        int digit = Character.digit(text.charAt(p), 10);
+        segSeconds *= 10;
+        segNanos = segNanos * 10 + digit * unitNanos;
+        segSeconds += segNanos / NANOS_PER_SECOND;
+        segNanos %= NANOS_PER_SECOND;
+        if (segSeconds > DURATION_SECONDS_MAX) {
+          throw outOfRangeDuration(text);
+        }
+      }
+
+      long fracNanos = 0;
+      for (int p = fracEnd - 1; p >= fracStart; p--) {
+        fracNanos = (Character.digit(text.charAt(p), 10) * unitNanos + fracNanos) / 10;
+      }
+
+      totalNanos += segNanos + fracNanos;
+      totalSeconds += segSeconds + totalNanos / NANOS_PER_SECOND;
+      totalNanos %= NANOS_PER_SECOND;
+      if (totalSeconds > DURATION_SECONDS_MAX) {
+        throw outOfRangeDuration(text);
+      }
+    }
+    return negative
+        ? Duration.ofSeconds(-totalSeconds, -totalNanos)
+        : Duration.ofSeconds(totalSeconds, totalNanos);
+  }
+
   /** Adds a duration to an instant. */
   public static Instant add(Instant ts, Duration dur) {
     Instant newInstant = ts.plus(dur);
@@ -102,10 +181,7 @@ public static Instant add(Instant ts, Duration dur) {
 
   /** Adds two durations */
   public static Duration add(Duration d1, Duration d2) {
-    Duration newDuration = d1.plus(d2);
-    checkValid(newDuration);
-
-    return newDuration;
+    return checkValid(d1.plus(d2));
   }
 
   /** Subtracts a duration to an instant. */
@@ -118,54 +194,72 @@ public static Instant subtract(Instant ts, Duration dur) {
 
   /** Subtract a duration from another. */
   public static Duration subtract(Duration d1, Duration d2) {
-    Duration newDuration = d1.minus(d2);
-    checkValid(newDuration);
+    return checkValid(d1.minus(d2));
+  }
 
-    return newDuration;
+  /** Calculates the difference between two instants. */
+  public static Duration between(Instant d1, Instant d2) {
+    return checkValid(Duration.between(d1, d2));
   }
 
-  /**
-   * Formats a {@link Duration} into a minimal seconds-based representation.
-   *
-   * <p>Note: follows {@code ProtoTimeUtils#toString(Duration)} implementation
-   */
+  /** Formats a {@link Duration} into a minimal seconds-based representation. */
   public static String toString(Duration duration) {
-    if (duration.isZero()) {
-      return "0s";
+    long seconds = duration.getSeconds();
+    int nanos = duration.getNano();
+    if (seconds < 0 && nanos > 0) {
+      seconds++;
+      nanos -= NANOS_PER_SECOND;
     }
+    return ProtoTimeUtils.formatDuration(seconds, nanos);
+  }
 
-    long totalNanos = duration.toNanos();
-    StringBuilder sb = new StringBuilder();
-
-    if (totalNanos < 0) {
-      sb.append('-');
-      totalNanos = -totalNanos;
+  private static int scanAsciiDigits(String text, int i) {
+    while (i < text.length() && isAsciiDigit(text.charAt(i))) {
+      i++;
     }
+    return i;
+  }
+
+  private static boolean isAsciiDigit(char c) {
+    return c >= '0' && c <= '9';
+  }
 
-    long seconds = totalNanos / 1_000_000_000;
-    int nanos = (int) (totalNanos % 1_000_000_000);
-
-    sb.append(seconds);
-
-    // Follows ProtoTimeUtils.toString(Duration) implementation
-    if (nanos > 0) {
-      sb.append('.');
-      if (nanos % 1_000_000 == 0) {
-        // Millisecond precision (3 digits)
-        int millis = nanos / 1_000_000;
-        sb.append(String.format(Locale.US, "%03d", millis));
-      } else if (nanos % 1_000 == 0) {
-        // Microsecond precision (6 digits)
-        int micros = nanos / 1_000;
-        sb.append(String.format(Locale.US, "%06d", micros));
-      } else {
-        // Nanosecond precision (9 digits)
-        sb.append(String.format(Locale.US, "%09d", nanos));
+  private static long parseUnitNanos(String text, int start, int end) {
+    int len = end - start;
+    if (len == 1) {
+      switch (text.charAt(start)) {
+        case 's':
+          return NANOS_PER_SECOND;
+        case 'm':
+          return 60L * NANOS_PER_SECOND;
+        case 'h':
+          return 3600L * NANOS_PER_SECOND;
+        default:
+          break;
+      }
+    } else if (len == 2 && text.charAt(start + 1) == 's') {
+      switch (text.charAt(start)) {
+        case 'n':
+          return 1L;
+        case 'u':
+        case '\u00b5':
+        case '\u03bc':
+          return 1_000L;
+        case 'm':
+          return 1_000_000L;
+        default:
+          break;
       }
     }
+    throw invalidDurationFormat();
+  }
+
+  private static IllegalArgumentException invalidDurationFormat() {
+    return new IllegalArgumentException("invalid duration format");
+  }
 
-    sb.append('s');
-    return sb.toString();
+  private static IllegalArgumentException outOfRangeDuration(String text) {
+    return new IllegalArgumentException("Duration is out of valid range: " + text);
   }
 
   /**
@@ -205,55 +299,29 @@ private static ZoneId timeZone(String tz) {
 
   /** Throws an {@link IllegalArgumentException} if the given {@link Timestamp} is not valid. */
   public static void checkValid(Instant instant) {
-    long seconds = instant.getEpochSecond();
+    checkSecondsValid(instant.getEpochSecond());
+  }
 
-    if (seconds < TIMESTAMP_SECONDS_MIN || seconds > TIMESTAMP_SECONDS_MAX) {
+  @CanIgnoreReturnValue
+  private static Duration checkValid(Duration duration) {
+    if (duration.compareTo(DURATION_MIN) < 0 || duration.compareTo(DURATION_MAX) > 0) {
       throw new IllegalArgumentException(
           Strings.lenientFormat(
-              "Timestamp is not valid. "
-                  + "Seconds (%s) must be in range [-62,135,596,800, +253,402,300,799]. "
-                  + "Nanos (%s) must be in range [0, +999,999,999].",
-              seconds, instant.getNano()));
+              "Duration is out of valid range [-315,576,000,000.999999999s,"
+                  + " +315,576,000,000.999999999s]: %s",
+              duration));
     }
+    return duration;
   }
 
-  /** Throws an {@link IllegalArgumentException} if the given {@link Duration} is not valid. */
-  private static void checkValid(Duration duration) {
-    long seconds = duration.getSeconds();
-    int nanos = duration.getNano();
-    if (!isDurationValid(seconds, nanos)) {
+  private static void checkSecondsValid(long seconds) {
+    if (seconds < TIMESTAMP_SECONDS_MIN || seconds > TIMESTAMP_SECONDS_MAX) {
       throw new IllegalArgumentException(
           Strings.lenientFormat(
-              "Duration is not valid. "
-                  + "Seconds (%s) must be in range [-315,576,000,000, +315,576,000,000]. "
-                  + "Nanos (%s) must be in range [-999,999,999, +999,999,999]. "
-                  + "Nanos must have the same sign as seconds",
-              seconds, nanos));
-    }
-  }
-
-  /**
-   * Returns true if the given number of seconds and nanos is a valid {@link Duration}. The {@code
-   * seconds} value must be in the range [-315,576,000,000, +315,576,000,000]. The {@code nanos}
-   * value must be in the range [-999,999,999, +999,999,999].
-   *
-   * <p><b>Note:</b> Durations less than one second are represented with a 0 {@code seconds} field
-   * and a positive or negative {@code nanos} field. For durations of one second or more, a non-zero
-   * value for the {@code nanos} field must be of the same sign as the {@code seconds} field.
-   */
-  private static boolean isDurationValid(long seconds, int nanos) {
-    if (seconds < DURATION_SECONDS_MIN || seconds > DURATION_SECONDS_MAX) {
-      return false;
-    }
-    if (nanos < -999999999L || nanos >= NANOS_PER_SECOND) {
-      return false;
-    }
-    if (seconds < 0 || nanos < 0) {
-      if (seconds > 0 || nanos > 0) {
-        return false;
-      }
+              "Timestamp is not valid. Seconds (%s) must be in range [-62,135,596,800,"
+                  + " +253,402,300,799].",
+              seconds));
     }
-    return true;
   }
 
   private DateTimeHelpers() {}