diff --git a/crates/warp_harness_usage/src/claude.rs b/crates/warp_harness_usage/src/claude.rs
index 063bf4d2444..6c0d05d5361 100644
--- a/crates/warp_harness_usage/src/claude.rs
+++ b/crates/warp_harness_usage/src/claude.rs
@@ -272,12 +272,17 @@ pub fn extract_claude<'a>(
 fn parse_usage(value: &Value, findings: &mut Findings) -> Option<Counters<6>> {
     if value
         .get("cache_creation")
-        .is_some_and(|partitions| !partitions.is_object())
+        .is_some_and(|partitions| !partitions.is_null() && !partitions.is_object())
     {
         findings.token(ReasonCode::InvalidData);
         return None;
     }
-    let usage = Counters::parse(value, PATHS, findings)?;
+    let usage = Counters::parse(
+        value,
+        PATHS,
+        &["/cache_read_input_tokens", "/cache_creation_input_tokens"],
+        findings,
+    )?;
     let [_, _, _, aggregate, short, long] = usage.values;
     if let (Some(aggregate), Some(short), Some(long)) = (aggregate, short, long)
         && short.checked_add(long) != Some(aggregate)
diff --git a/crates/warp_harness_usage/src/claude_tests.rs b/crates/warp_harness_usage/src/claude_tests.rs
index 66b3eb49362..76ccb5f2a3c 100644
--- a/crates/warp_harness_usage/src/claude_tests.rs
+++ b/crates/warp_harness_usage/src/claude_tests.rs
@@ -91,6 +91,139 @@ fn response(id: &str, usage: Value, content: Value) -> Value {
     json!({"type":"assistant","message":{"id":id,"model":"claude-a","usage":usage,"content":content}})
 }
 
+#[test]
+fn nullable_cache_fields_preserve_known_usage_attribution_and_tools() {
+    for (field, expected) in [
+        (
+            "cache_creation",
+            json!({"input_tokens":100,"output_tokens":0,"cache_read_input_tokens":4096,"cache_creation_input_tokens":0}),
+        ),
+        (
+            "cache_read_input_tokens",
+            json!({"input_tokens":100,"output_tokens":0,"cache_creation_input_tokens":0,"cache_creation":{"ephemeral_5m_input_tokens":0,"ephemeral_1h_input_tokens":0}}),
+        ),
+        (
+            "cache_creation_input_tokens",
+            json!({"input_tokens":100,"output_tokens":0,"cache_read_input_tokens":4096,"cache_creation":{"ephemeral_5m_input_tokens":0,"ephemeral_1h_input_tokens":0}}),
+        ),
+    ] {
+        let mut usage = json!({
+            "input_tokens":100,"output_tokens":0,"cache_read_input_tokens":4096,
+            "cache_creation_input_tokens":0,
+            "cache_creation":{"ephemeral_5m_input_tokens":0,"ephemeral_1h_input_tokens":0},
+            "service_tier":"standard"
+        });
+        usage[field] = Value::Null;
+        let snapshot = capture(&[response(
+            "a",
+            usage,
+            json!([{"type":"tool_use","id":"t","name":"Read"}]),
+        )]);
+        assert_eq!(
+            serde_json::to_value(&snapshot.payload).unwrap(),
+            json!({
+                "usage":expected,
+                "attribution":[{"model":"claude-a","service_tier":"standard","usage":expected}],
+                "toolCalls":{"total":1,"byName":{"Read":1}}
+            }),
+            "{field}"
+        );
+        assert_eq!(snapshot.coverage.token_status, CoverageStatus::Known);
+        assert_eq!(snapshot.coverage.tool_status, CoverageStatus::Known);
+        assert!(snapshot.diagnostics.reasons.is_empty(), "{field}");
+    }
+}
+
+#[test]
+fn null_cache_counter_in_one_response_makes_its_observed_total_partial() {
+    let snapshot = capture(&[
+        response(
+            "a",
+            json!({"input_tokens":10,"output_tokens":1,"cache_read_input_tokens":100}),
+            json!([]),
+        ),
+        response(
+            "b",
+            json!({"input_tokens":20,"output_tokens":2,"cache_read_input_tokens":null}),
+            json!([]),
+        ),
+    ]);
+    assert_eq!(
+        serde_json::to_value(&snapshot.payload).unwrap()["usage"],
+        json!({"input_tokens":30,"output_tokens":3,"cache_read_input_tokens":100})
+    );
+    assert_eq!(snapshot.coverage.token_status, CoverageStatus::Partial);
+    assert_eq!(snapshot.coverage.tool_status, CoverageStatus::Known);
+    assert_eq!(
+        snapshot.diagnostics.reasons,
+        [(ReasonCode::IncompleteInput, 1)].into()
+    );
+}
+
+#[test]
+fn later_null_cache_fields_do_not_replace_a_complete_response() {
+    let known = json!({
+        "input_tokens":100,"output_tokens":2,"cache_read_input_tokens":4096,
+        "cache_creation_input_tokens":15,
+        "cache_creation":{"ephemeral_5m_input_tokens":10,"ephemeral_1h_input_tokens":5}
+    });
+    for field in [
+        "cache_creation",
+        "cache_read_input_tokens",
+        "cache_creation_input_tokens",
+    ] {
+        let mut later = known.clone();
+        later[field] = Value::Null;
+        let snapshot = capture(&[
+            response("a", known.clone(), json!([])),
+            response("a", later, json!([])),
+        ]);
+        assert_eq!(
+            serde_json::to_value(&snapshot.payload).unwrap()["usage"],
+            json!({
+                "input_tokens":100,"output_tokens":2,"cache_read_input_tokens":4096,
+                "cache_creation_input_tokens":15,
+                "cache_creation":{"ephemeral_5m_input_tokens":10,"ephemeral_1h_input_tokens":5}
+            }),
+            "{field}"
+        );
+        assert_eq!(snapshot.coverage.token_status, CoverageStatus::Known);
+        assert!(snapshot.diagnostics.reasons.is_empty(), "{field}");
+    }
+}
+
+#[test]
+fn nullable_cache_fields_do_not_relax_other_counter_validation() {
+    for (path, value) in [
+        ("/cache_read_input_tokens", json!("0")),
+        ("/cache_read_input_tokens", json!(-1)),
+        ("/cache_creation_input_tokens", json!("0")),
+        ("/cache_creation_input_tokens", json!(-1)),
+        ("/cache_creation", json!("0")),
+        ("/cache_creation", json!(-1)),
+        ("/input_tokens", Value::Null),
+        ("/output_tokens", Value::Null),
+        ("/cache_creation/ephemeral_5m_input_tokens", Value::Null),
+        ("/cache_creation/ephemeral_1h_input_tokens", Value::Null),
+    ] {
+        let mut usage = json!({
+            "input_tokens":100,"output_tokens":0,"cache_read_input_tokens":4096,
+            "cache_creation_input_tokens":0,
+            "cache_creation":{"ephemeral_5m_input_tokens":0,"ephemeral_1h_input_tokens":0}
+        });
+        *usage.pointer_mut(path).unwrap() = value;
+        let snapshot = capture(&[response("a", usage, json!([]))]);
+        assert_eq!(
+            serde_json::to_value(&snapshot.payload).unwrap(),
+            json!({"toolCalls":{"total":0,"byName":{}}}),
+            "{path}"
+        );
+        assert_eq!(snapshot.coverage.token_status, CoverageStatus::Unavailable);
+        assert_eq!(snapshot.coverage.tool_status, CoverageStatus::Known);
+        assert_eq!(snapshot.diagnostics.reasons[&ReasonCode::InvalidData], 1);
+    }
+}
+
 #[test]
 fn evolving_responses_do_not_deduplicate_distinct_tool_blocks() {
     let entries = parse_jsonl(
diff --git a/crates/warp_harness_usage/src/codex.rs b/crates/warp_harness_usage/src/codex.rs
index 380a572e940..1f2428a48dc 100644
--- a/crates/warp_harness_usage/src/codex.rs
+++ b/crates/warp_harness_usage/src/codex.rs
@@ -257,7 +257,7 @@ fn observe_checkpoint(
 }
 
 fn parse_usage(value: &Value, findings: &mut Findings) -> Option<Counters<6>> {
-    let usage = Counters::parse(value, PATHS, findings)?;
+    let usage = Counters::parse(value, PATHS, &[], findings)?;
     let [input, cached, cache_write, output, reasoning, total] = usage.values;
     let invalid = matches!((input, cached), (Some(input), Some(cached)) if cached > input)
         || matches!((input, cache_write), (Some(input), Some(cache_write)) if cache_write > input)
diff --git a/crates/warp_harness_usage/src/codex_tests.rs b/crates/warp_harness_usage/src/codex_tests.rs
index 000e52e59ac..fce70f46172 100644
--- a/crates/warp_harness_usage/src/codex_tests.rs
+++ b/crates/warp_harness_usage/src/codex_tests.rs
@@ -346,6 +346,29 @@ fn counter_bounds_and_absence_survive_serialization() {
     );
 }
 
+#[test]
+fn null_counters_preserve_the_valid_prefix() {
+    for field in [
+        "input_tokens",
+        "cached_input_tokens",
+        "cache_write_input_tokens",
+        "output_tokens",
+        "reasoning_output_tokens",
+        "total_tokens",
+    ] {
+        let mut invalid = checkpoint(100, 90);
+        invalid["payload"]["info"]["total_token_usage"][field] = Value::Null;
+        let snapshot = capture(&[checkpoint(10, 10), invalid]);
+        assert_eq!(
+            serde_json::to_value(&snapshot.payload).unwrap()["usage"],
+            json!({"total_tokens":10}),
+            "{field}"
+        );
+        assert_eq!(snapshot.coverage.token_status, CoverageStatus::Partial);
+        assert_eq!(snapshot.diagnostics.reasons[&ReasonCode::InvalidData], 1);
+    }
+}
+
 #[test]
 fn excessive_cache_write_totals_preserve_the_valid_prefix() {
     for input in [0, 100, i64::MAX - 1] {
diff --git a/crates/warp_harness_usage/src/counters.rs b/crates/warp_harness_usage/src/counters.rs
index 700470c9a48..161524d9597 100644
--- a/crates/warp_harness_usage/src/counters.rs
+++ b/crates/warp_harness_usage/src/counters.rs
@@ -21,8 +21,13 @@ impl<const N: usize> Default for Counters<N> {
 }
 
 impl<const N: usize> Counters<N> {
-    /// Parse known nonnegative counters while preserving absent fields as unknown.
-    pub(crate) fn parse(value: &Value, paths: [&str; N], findings: &mut Findings) -> Option<Self> {
+    /// Parse nonnegative counters, preserving absent and explicitly nullable fields as unknown.
+    pub(crate) fn parse(
+        value: &Value,
+        paths: [&str; N],
+        nullable_paths: &[&str],
+        findings: &mut Findings,
+    ) -> Option<Self> {
         if !value.is_object() {
             findings.token(ReasonCode::InvalidData);
             return None;
@@ -30,6 +35,9 @@ impl<const N: usize> Counters<N> {
         let mut result = Self::default();
         for (index, path) in paths.into_iter().enumerate() {
             if let Some(value) = value.pointer(path) {
+                if value.is_null() && nullable_paths.contains(&path) {
+                    continue;
+                }
                 match value.as_i64().filter(|count| *count >= 0) {
                     Some(count) => result.values[index] = Some(count),
                     None => {