previous_interaction_id chain re-roots mid-conversation, then rejects a valid function_result

Interactions API: `previous_interaction_id` chain re-roots mid-conversation, then rejects a valid `function_result`

Model: gemini-3.8-flash · Endpoint: POST /v1beta/interactions (streaming) · SDK: google-genai 2.8.0 and 2.25.0 (same result) · Reproduced: 2026-09-22

Summary

In a tool-calling conversation chained only with previous_interaction_id, the server
sometimes starts a new conversation root partway through. Two interactions later,
answering the pending function_call with a function_result fails with:

invalid_request: Please ensure that function response turn comes immediately after a function call turn. Got function response with name 'run_travel_code'.

The client's request is valid. The interaction being chained off ends in a function_call,
and the function_result answers that call's id.

How the re-root shows up

An interaction id is v1_<urlsafe base64 protobuf>: field 1 is the conversation root id and
field 2 is the interaction's own id. They should be equal only on a conversation's first
interaction. In failing runs they become equal mid-chain (RE-ROOTED below). The
rejection follows two interactions later, when the rebuilt history seems to start with a
function_result whose function_call belongs to the old root.

Evidence it is server-side

Checked against the rejected interaction:

Its stored steps are function_result -> thought -> function_call, so answering it is legal.
Replaying the identical request is rejected every time; it isn't transient.
Plain-text input chained to the same interaction is accepted.
The same history flattened from interactions.get and sent explicitly, without
previous_interaction_id, is accepted. Same content, so only the server-side chain
reconstruction is wrong.

Not caused by the SDK: reproduces on 2.8.0 and 2.25.0, and toggling the api-revision
header 2.8.0 sends makes no difference. Not caused by timing: reproduces with no delay
between turns. It happens in roughly 10-50% of conversations, varying from run to run.

Repro

Attached gemini_reroot_repro.py (self-contained; needs GEMINI_API_KEY):

uv run gemini_reroot_repro.py

It exits 1 when it catches the bug. Each run may not catch it; re-run or pass --conversations 16.

Example run

Excerpt: conversations that hit the bug are shown in full; 8 clean and 2 re-rooted without a rejection omitted. The full log is attached as gemini_reroot_bug_report.log.

==============================================================================
Gemini Interactions API -- conversation re-root breaks previous_interaction_id
==============================================================================
google-genai : 2.25.0
python       : 3.13.11
model        : gemini-3.8-flash
started (UTC): 2026-09-22T19:43:36Z

An interaction id is v1_<base64 protobuf>: field 1 is the conversation ROOT id, field 2
is the interaction's OWN id. They should match only on a conversation's first turn.
Running 12 conversations concurrently; each prints its table when it
finishes.  >> = re-rooted (root == self mid-chain)   XX = function_result rejected

Conversation 11 -- HIT THE BUG
    turn  status      calls  root (field 1)           self (field 2)           chained from (prev self)  interaction id
-----------------------------------------------------------------------------------------------------------------------
    1     start       1      aNqyapjKNdW7qtsPq9nq4QU  aNqyapjKNdW7qtsPq9nq4QU  (none)                    v1_ChdhTnF5YXBqS05kVzdxdHNQcTlucTRRVRIXYU5xeWFwaktOZFc3cXRzUHE5bnE0UVU
>>  2     RE-ROOTED   1      a9qyaqDwEYjsz7IPiY2foQU  a9qyaqDwEYjsz7IPiY2foQU  aNqyapjKNdW7qtsPq9nq4QU   v1_ChdhOXF5YXFEd0VZanN6N0lQaVkyZm9RVRIXYTlxeWFxRHdFWWpzejdJUGlZMmZvUVU
    3     ok          1      a9qyaqDwEYjsz7IPiY2foQU  bdqyasjfIfeHqtsPo5LB-Qk  a9qyaqDwEYjsz7IPiY2foQU   v1_ChdhOXF5YXFEd0VZanN6N0lQaVkyZm9RVRIXYmRxeWFzamZJZmVIcXRzUG81TEItUWs
XX  4     REJECTED    -      -                        -                        bdqyasjfIfeHqtsPo5LB-Qk   (rejected - no interaction created)

>> RE-ROOTED at turn 2: root (field 1) became the interaction's own id, so the server started a new conversation root mid-chain.
XX REJECTED at turn 4: submitting the function_result chained off the previous interaction failed with:
   Please ensure that function response turn comes immediately after a function call turn. Got function response with name 'run_travel_code'.

Conversation 6 -- HIT THE BUG
    turn  status      calls  root (field 1)           self (field 2)           chained from (prev self)  interaction id
-----------------------------------------------------------------------------------------------------------------------
    1     start       1      adqyavisAbTmz7IPqLPtqQQ  adqyavisAbTmz7IPqLPtqQQ  (none)                    v1_ChdhZHF5YXZpc0FiVG16N0lQcUxQdHFRURIXYWRxeWF2aXNBYlRtejdJUHFMUHRxUVE
    2     ok          1      adqyavisAbTmz7IPqLPtqQQ  atqyaovUOMGoqtsPp9-n8A0  adqyavisAbTmz7IPqLPtqQQ   v1_ChdhZHF5YXZpc0FiVG16N0lQcUxQdHFRURIXYXRxeWFvdlVPTUdvcXRzUHA5LW44QTA
    3     ok          1      adqyavisAbTmz7IPqLPtqQQ  bdqyauPqAZOxqtsPo_6E6A0  atqyaovUOMGoqtsPp9-n8A0   v1_ChdhZHF5YXZpc0FiVG16N0lQcUxQdHFRURIXYmRxeWF1UHFBWk94cXRzUG9fNkU2QTA
>>  4     RE-ROOTED   1      cNqyata5JY6sz7IP8K7uoAg  cNqyata5JY6sz7IP8K7uoAg  bdqyauPqAZOxqtsPo_6E6A0   v1_ChdjTnF5YXRhNUpZNnN6N0lQOEs3dW9BZxIXY05xeWF0YTVKWTZzejdJUDhLN3VvQWc
    5     ok          1      cNqyata5JY6sz7IP8K7uoAg  dNqyauqgPOzzz7IP5Z2x4AQ  cNqyata5JY6sz7IP8K7uoAg   v1_ChdjTnF5YXRhNUpZNnN6N0lQOEs3dW9BZxIXZE5xeWF1cWdQT3p6ejdJUDVaMng0QVE
XX  6     REJECTED    -      -                        -                        dNqyauqgPOzzz7IP5Z2x4AQ   (rejected - no interaction created)

>> RE-ROOTED at turn 4: root (field 1) became the interaction's own id, so the server started a new conversation root mid-chain.
XX REJECTED at turn 6: submitting the function_result chained off the previous interaction failed with:
   Please ensure that function response turn comes immediately after a function call turn. Got function response with name 'run_travel_code'.

==============================================================================
re-rooted mid-chain : 4/12
rejected submissions: 2/12
==============================================================================

Controls against the rejected interaction
   v1_ChdjTnF5YXRhNUpZNnN6N0lQOEs3dW9BZxIXZE5xeWF1cWdQT3p6ejdJUDVaMng0QVE
  [0] its stored steps: function_result -> thought -> function_call
      it ends in a function_call, so answering with a function_result is legal
  [1.1] replay of the rejected request: rejected again
  [1.2] replay of the rejected request: rejected again
  [2] same interaction with PLAIN TEXT input: accepted
  [3] SAME history sent EXPLICITLY (15 steps, no previous_interaction_id): ACCEPTED
      => the content is valid; only the server's chain reconstruction is wrong

gemini_reroot_bug_report.log

gemini_reroot_repro.py

@JasonSteving99

Hi @JasonSteving99,
Thank you for providing such a detailed bug report, logs, and the self-contained reproduction script (gemini_reroot_repro.py). I ran the reproduction script across multiple test runs with concurrent multi-turn conversations (8 to 16 parallel chains) targeting gemini-3.8-flash on the Interactions API (POST /v1beta/interactions).

In our recent test runs, all conversations completed cleanly without encountering the re-rooting issue.

Could you please re-run your repro script and let us know if you are still able to reproduce the issue..?
Thanks!

@Venkaiahbabuneelam

Hey @Venkaiahbabuneelam this is still happening. I'm not the only one running into this issue, colleagues have run into it as well. I attached a rerun that I ran just now.

rerun.log

Hold Gemini conversations in the workflow, and fail Gemini 4xx errors…

Anyone look into this? We had to workaround this by simply not using the interactions API with server managed context history and instead managing it manually on our side.

==============================================================================
Gemini Interactions API -- conversation re-root breaks previous_interaction_id

google-genai : 2.28.0
python : 3.13.7
model : gemini-3.8-flash
started (UTC): 2026-10-08T06:18:24Z

An interaction id is v1_: field 1 is the conversation ROOT id, field 2
is the interaction's OWN id. They should match only on a conversation's first turn.
Running 8 conversations concurrently; each prints its table when it
finishes. >> = re-rooted (root == self mid-chain) XX = function_result rejected