diff --git a/crates/omnigraph-cli/src/main.rs b/crates/omnigraph-cli/src/main.rs
index 742c75c..a7c762b 100644
--- a/crates/omnigraph-cli/src/main.rs
+++ b/crates/omnigraph-cli/src/main.rs
@@ -18,7 +18,7 @@ use omnigraph_compiler::{
 };
 use omnigraph_server::api::{
     BranchCreateOutput, BranchCreateRequest, BranchDeleteOutput, BranchListOutput,
-    BranchMergeOutput, BranchMergeRequest, ChangeOutput, ChangeRequest, CommitListOutput,
+    BranchMergeOutput, BranchMergeRequest, ChangeOutput, CommitListOutput,
     CommitOutput, ErrorOutput, ExportRequest, IngestOutput, IngestRequest, ReadOutput, ReadRequest,
     SchemaApplyOutput, SchemaApplyRequest, SchemaOutput, SnapshotOutput, SnapshotTableOutput,
     commit_output, ingest_output, read_output, schema_apply_output, snapshot_payload,
@@ -1636,6 +1636,33 @@ async fn execute_change(
     })
 }
 
+/// Build the JSON body for `POST /change` using the legacy wire shape.
+///
+/// `ChangeRequest`'s Rust field names are now `query` / `name` (the canonical
+/// wire shape going forward), but old `omnigraph-server` builds still require
+/// the legacy `query_source` / `query_name` keys on `/change`. Hand-rolling
+/// the JSON with the legacy names keeps a newer CLI talking to an older
+/// server intact -- the same byte-stability contract we apply to
+/// `execute_read_remote` against `/read`.
+fn legacy_change_request_body(
+    query_source: &str,
+    query_name: Option<&str>,
+    branch: &str,
+    params_json: Option<&Value>,
+) -> Value {
+    let mut body = serde_json::json!({
+        "query_source": query_source,
+        "branch": branch,
+    });
+    if let Some(name) = query_name {
+        body["query_name"] = Value::String(name.to_string());
+    }
+    if let Some(params) = params_json {
+        body["params"] = params.clone();
+    }
+    body
+}
+
 async fn execute_change_remote(
     client: &reqwest::Client,
     uri: &str,
@@ -1649,12 +1676,12 @@ async fn execute_change_remote(
         client,
         Method::POST,
         remote_url(uri, "/change"),
-        Some(serde_json::to_value(ChangeRequest {
-            query: query_source.to_string(),
-            name: query_name.map(ToOwned::to_owned),
-            params: params_json.cloned(),
-            branch: Some(branch.to_string()),
-        })?),
+        Some(legacy_change_request_body(
+            query_source,
+            query_name,
+            branch,
+            params_json,
+        )),
         bearer_token,
     )
     .await
@@ -2627,14 +2654,62 @@ mod tests {
     use std::fs;
 
     use super::{
-        DEFAULT_BEARER_TOKEN_ENV, apply_bearer_token, bearer_token_from_env_file, load_cli_config,
-        load_env_file_into_process, normalize_bearer_token, parse_env_assignment,
-        resolve_remote_bearer_token,
+        DEFAULT_BEARER_TOKEN_ENV, apply_bearer_token, bearer_token_from_env_file,
+        legacy_change_request_body, load_cli_config, load_env_file_into_process,
+        normalize_bearer_token, parse_env_assignment, resolve_remote_bearer_token,
     };
     use omnigraph_server::load_config;
     use reqwest::header::AUTHORIZATION;
+    use serde_json::json;
     use tempfile::tempdir;
 
+    #[test]
+    fn legacy_change_request_body_uses_legacy_field_names() {
+        // `execute_change_remote` hits `POST /change`, which old
+        // `omnigraph-server` builds deserialize as `ChangeRequest` with
+        // **required** `query_source` and optional `query_name` keys.
+        // Newer servers accept both spellings via serde alias, but a
+        // newer CLI must still emit the legacy keys on the wire so it
+        // can talk to an old server during a rolling upgrade.
+        let body = legacy_change_request_body(
+            "query insert_person($n: String) { insert Person { name: $n } }",
+            Some("insert_person"),
+            "main",
+            Some(&json!({ "n": "Alice" })),
+        );
+        assert_eq!(
+            body["query_source"].as_str(),
+            Some("query insert_person($n: String) { insert Person { name: $n } }"),
+        );
+        assert_eq!(body["query_name"].as_str(), Some("insert_person"));
+        assert_eq!(body["branch"].as_str(), Some("main"));
+        assert_eq!(body["params"]["n"].as_str(), Some("Alice"));
+        // Crucially, the **new** field names must NOT appear -- old
+        // servers would silently treat them as unknown fields and then
+        // fail on missing required `query_source`.
+        assert!(
+            body.get("query").is_none(),
+            "legacy /change body must not carry the renamed `query` key; got {body}"
+        );
+        assert!(
+            body.get("name").is_none(),
+            "legacy /change body must not carry the renamed `name` key; got {body}"
+        );
+    }
+
+    #[test]
+    fn legacy_change_request_body_omits_optional_fields_when_unset() {
+        let body = legacy_change_request_body(
+            "query find() { match { $p: Person } return { $p.name } }",
+            None,
+            "main",
+            None,
+        );
+        assert_eq!(body["branch"].as_str(), Some("main"));
+        assert!(body.get("query_name").is_none());
+        assert!(body.get("params").is_none());
+    }
+
     #[test]
     fn apply_bearer_token_adds_header_when_configured() {
         let client = reqwest::Client::new();
diff --git a/crates/omnigraph-server/src/api.rs b/crates/omnigraph-server/src/api.rs
index 9498c38..6699a6b 100644
--- a/crates/omnigraph-server/src/api.rs
+++ b/crates/omnigraph-server/src/api.rs
@@ -252,13 +252,15 @@ pub struct ReadRequest {
 ///
 /// Friendlier-named alternative to [`ReadRequest`] for ad-hoc reads and
 /// AI-agent integration. Mutations are rejected with 400 — use `POST
-/// /change` for write queries. Field names are deliberately short
-/// (`query`, `name`) to match the GQ keyword and the CLI `-e` flag.
+/// /mutate` (or its deprecated alias `POST /change`) for write queries.
+/// Field names are deliberately short (`query`, `name`) to match the GQ
+/// keyword and the CLI `-e` flag.
 #[derive(Debug, Clone, Serialize, Deserialize, ToSchema)]
 pub struct QueryRequest {
     /// GQ read-query source. May declare one or more named queries; pick one
     /// with `name` when more than one is declared. Mutations
-    /// (`insert`/`update`/`delete`) get 400 — use `POST /change` instead.
+    /// (`insert`/`update`/`delete`) get 400 — use `POST /mutate` (or its
+    /// deprecated alias `POST /change`) instead.
     #[schema(example = "query get_person($name: String) {\n    match {\n        $p: Person { name: $name }\n    }\n    return { $p.name, $p.age }\n}")]
     pub query: String,
     /// Name of the query to run when `query` declares multiple. Optional when
diff --git a/crates/omnigraph-server/src/lib.rs b/crates/omnigraph-server/src/lib.rs
index c9cd9d0..618677f 100644
--- a/crates/omnigraph-server/src/lib.rs
+++ b/crates/omnigraph-server/src/lib.rs
@@ -1026,7 +1026,7 @@ async fn server_read(
     request_body = QueryRequest,
     responses(
         (status = 200, description = "Query results", body = ReadOutput),
-        (status = 400, description = "Bad request - also returned when the query body contains mutations; use POST /change for write queries", body = ErrorOutput),
+        (status = 400, description = "Bad request - also returned when the query body contains mutations; use POST /mutate (or its deprecated alias POST /change) for write queries", body = ErrorOutput),
         (status = 401, description = "Unauthorized", body = ErrorOutput),
         (status = 403, description = "Forbidden", body = ErrorOutput),
     ),
@@ -1037,9 +1037,10 @@ async fn server_read(
 /// Designed for ad-hoc exploration and AI-agent tool-use: short field
 /// names (`query`, `name`) match the CLI `-e` flag and the GQ `query`
 /// keyword. Mutations (`insert`/`update`/`delete`) are rejected with 400
-/// -- use `POST /change` for write queries. Otherwise behaves
-/// identically to `POST /read`: same target semantics (branch xor
-/// snapshot), same Cedar action (Read), same response shape.
+/// -- use `POST /mutate` (or its deprecated alias `POST /change`) for
+/// write queries. Otherwise behaves identically to `POST /read`: same
+/// target semantics (branch xor snapshot), same Cedar action (Read),
+/// same response shape.
 async fn server_query(
     State(state): State<AppState>,
     actor: Option<Extension<AuthenticatedActor>>,
@@ -1080,7 +1081,7 @@ async fn server_query(
         .map_err(|err| ApiError::bad_request(err.to_string()))?;
     if !query_decl.mutations.is_empty() {
         return Err(ApiError::bad_request(format!(
-            "query '{}' contains mutations (insert/update/delete); use POST /change for write queries",
+            "query '{}' contains mutations (insert/update/delete); use POST /mutate for write queries",
             query_decl.name
         )));
     }
diff --git a/crates/omnigraph-server/tests/openapi.rs b/crates/omnigraph-server/tests/openapi.rs
index f6968d3..70824fb 100644
--- a/crates/omnigraph-server/tests/openapi.rs
+++ b/crates/omnigraph-server/tests/openapi.rs
@@ -485,7 +485,7 @@ fn query_endpoint_documents_mutation_400() {
     let four_hundred = &doc["paths"]["/query"]["post"]["responses"]["400"];
     let description = four_hundred["description"].as_str().unwrap_or_default();
     assert!(
-        description.contains("mutations") || description.contains("POST /change"),
+        description.contains("mutations") || description.contains("POST /mutate"),
         "expected /query 400 response to mention mutation rejection, got: {description}"
     );
 }
diff --git a/crates/omnigraph-server/tests/server.rs b/crates/omnigraph-server/tests/server.rs
index bbf6019..0b25840 100644
--- a/crates/omnigraph-server/tests/server.rs
+++ b/crates/omnigraph-server/tests/server.rs
@@ -2060,8 +2060,8 @@ async fn query_endpoint_rejects_mutation_with_400() {
     assert_eq!(status, StatusCode::BAD_REQUEST);
     let err = body["error"].as_str().unwrap_or_default();
     assert!(
-        err.contains("contains mutations") && err.contains("POST /change"),
-        "expected mutation-rejection message, got: {err}"
+        err.contains("contains mutations") && err.contains("POST /mutate"),
+        "expected mutation-rejection message pointing at canonical /mutate, got: {err}"
     );
 }
 
diff --git a/openapi.json b/openapi.json
index 0f335bb..8e36231 100644
--- a/openapi.json
+++ b/openapi.json
@@ -778,7 +778,7 @@
           "queries"
         ],
         "summary": "Execute an inline read query (friendlier-named alternative to `POST /read`).",
-        "description": "Designed for ad-hoc exploration and AI-agent tool-use: short field\nnames (`query`, `name`) match the CLI `-e` flag and the GQ `query`\nkeyword. Mutations (`insert`/`update`/`delete`) are rejected with 400\n-- use `POST /change` for write queries. Otherwise behaves\nidentically to `POST /read`: same target semantics (branch xor\nsnapshot), same Cedar action (Read), same response shape.",
+        "description": "Designed for ad-hoc exploration and AI-agent tool-use: short field\nnames (`query`, `name`) match the CLI `-e` flag and the GQ `query`\nkeyword. Mutations (`insert`/`update`/`delete`) are rejected with 400\n-- use `POST /mutate` (or its deprecated alias `POST /change`) for\nwrite queries. Otherwise behaves identically to `POST /read`: same\ntarget semantics (branch xor snapshot), same Cedar action (Read),\nsame response shape.",
         "operationId": "query",
         "requestBody": {
           "content": {
@@ -802,7 +802,7 @@
             }
           },
           "400": {
-            "description": "Bad request - also returned when the query body contains mutations; use POST /change for write queries",
+            "description": "Bad request - also returned when the query body contains mutations; use POST /mutate (or its deprecated alias POST /change) for write queries",
             "content": {
               "application/json": {
                 "schema": {
@@ -1611,7 +1611,7 @@
       },
       "QueryRequest": {
         "type": "object",
-        "description": "Inline read-query request for `POST /query`.\n\nFriendlier-named alternative to [`ReadRequest`] for ad-hoc reads and\nAI-agent integration. Mutations are rejected with 400 — use `POST\n/change` for write queries. Field names are deliberately short\n(`query`, `name`) to match the GQ keyword and the CLI `-e` flag.",
+        "description": "Inline read-query request for `POST /query`.\n\nFriendlier-named alternative to [`ReadRequest`] for ad-hoc reads and\nAI-agent integration. Mutations are rejected with 400 — use `POST\n/mutate` (or its deprecated alias `POST /change`) for write queries.\nField names are deliberately short (`query`, `name`) to match the GQ\nkeyword and the CLI `-e` flag.",
         "required": [
           "query"
         ],
@@ -1635,7 +1635,7 @@
           },
           "query": {
             "type": "string",
-            "description": "GQ read-query source. May declare one or more named queries; pick one\nwith `name` when more than one is declared. Mutations\n(`insert`/`update`/`delete`) get 400 — use `POST /change` instead.",
+            "description": "GQ read-query source. May declare one or more named queries; pick one\nwith `name` when more than one is declared. Mutations\n(`insert`/`update`/`delete`) get 400 — use `POST /mutate` (or its\ndeprecated alias `POST /change`) instead.",
             "example": "query get_person($name: String) {\n    match {\n        $p: Person { name: $name }\n    }\n    return { $p.name, $p.age }\n}"
           },
           "snapshot": {