> ## Documentation Index > Fetch the complete documentation index at: https://phidatainc-feat-checkpointing.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Fork a Run > Rewind to a message boundary and explore an alternative path. Sibling run in the same session. A fork is a sibling run within the same session, started from a chosen message boundary of an existing run. Use it to explore alternative paths, run evals from a known-good state, or A/B-test instructions. ## Basic Usage ```python theme={null} fork = agent.continue_run( run_id="run-abc", session_id="sess-xyz", continue_from="last_user", fork=True, input="Try a different approach this time", ) ``` The new run has a fresh `run_id`, `forked_from_run_id` pointing at the source, and `forked_from_message_index` recording where it cut. ## Where to Fork From `continue_from` chooses the message boundary. | Value | What it keeps | | ------------- | ----------------------------------------------------------------------------------------------------------- | | `"end"` | Full transcript. Use to continue a completed run with a new turn. | | `"last_user"` | Drop everything past the last user message. Tools will be re-invoked. | | `K: int` | Keep `messages[:K]`. Pair-safe: indices that split a tool batch snap down to the boundary before the batch. | For valid integer indices on a specific run, call the [checkpoints endpoint](/run-control/api-reference). Every index it returns is pair-safe. ## Forking vs Regenerating | | Fork | Regenerate | | ----------------- | ---------------------------------- | ---------------------------------------------------- | | What's kept | Up to `continue_from` (you choose) | Everything up to last user message + tool exchanges | | Tools re-invoked? | Depends on cut point | No. Intermediate tool exchanges survive. | | Source visibility | Always visible | `replace_original=True` hides; `False` keeps visible | | Use case | "Try a different reasoning path" | "Redo the final summary" | If you want a cheap "try again with steering" without re-running tools, use [Regenerate](/run-control/regenerate). If you want to rewind further (drop tools, drop intermediate turns, change the prompt entirely), fork. ## Auto-Fork on COMPLETED Continuing a completed run always produces a new `run_id`, even without `fork=True`: ```python theme={null} # Source is COMPLETED. /continue produces a new run_id automatically. new_run = agent.continue_run( run_id="run-abc", session_id="sess-xyz", input="Now compare with Tokyo", ) ``` The 1-run-1-loop invariant: a completed model loop cannot be overwritten. The new turn always lands on a new run row. ## Pair-Safe Truncation Integer `continue_from=K` snaps down to a "pair-safe" boundary when `K` lands mid-tool-batch. Given the transcript: ``` [1] user [2] assistant tool_calls=[tc1, tc2, tc3] [3] tool: result for tc1 [4] tool: result for tc2 [5] tool: result for tc3 [6] assistant: final reply ``` | `continue_from=K` | Actual boundary | Why | | ----------------- | --------------- | ---------------------------------------------- | | 1 | 1 | Clean cut | | 2 | 1 | Would orphan assistant tool\_calls | | 3 | 1 | Mid-batch (tc2, tc3 results not yet in prefix) | | 4 | 1 | Mid-batch (tc3 result not yet in prefix) | | 5 | 5 | Whole batch present | | 6 | 6 | Full transcript | The fork response's `forked_from_message_index` reflects the actual boundary used. If it differs from what you sent, the dispatch snapped the index down. Indices returned by the [checkpoints endpoint](/run-control/api-reference) are always pair-safe by construction. ## Teams `Team.continue_run(fork=True, continue_from=...)` works the same way: ```python theme={null} fork = team.continue_run( run_id="team-run-abc", session_id="team-sess-xyz", continue_from="last_user", fork=True, input="What if we routed differently?", ) ``` The forked team is a new run in the same session. Member runs from the original team stay attached to the original via `parent_run_id`. The fork starts fresh and may produce new member runs. ## HTTP ```bash theme={null} curl -X POST "$HOST/agents/{agent_id}/runs/{run_id}/continue" \ -F "session_id=sess-xyz" \ -F "continue_from=last_user" \ -F "fork=true" \ -F "input=Try a different approach" ``` `continue_from` accepts `"end"`, `"last_user"`, or a numeric string (e.g. `"4"`). ## Examples ### Agents | Example | What it shows | | --------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------- | | [Fork a run](https://github.com/agno-agi/agno/blob/main/cookbook/02_agents/20_time_travel/02_fork_run.py) | `fork=True, continue_from=...` to clone a run at a chosen boundary. The forked run lives next to the original in the same session. | | [Continue from a boundary](https://github.com/agno-agi/agno/blob/main/cookbook/02_agents/20_time_travel/01_continue_from.py) | All four `continue_from` forms (`"end"`, `"last_user"`, integer, `regenerate=True`) including the auto-fork-on-completed case. | | [Checkpoint endpoints](https://github.com/agno-agi/agno/blob/main/cookbook/02_agents/18_checkpointing/03_checkpoint_endpoints.py) | How to discover valid integer indices: call `GET /checkpoints`, then feed `message_index` back into `continue_from=K`. Every index returned is pair-safe. | ### Teams | Example | What it shows | | --------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------- | | [Fork a team run](https://github.com/agno-agi/agno/blob/main/cookbook/03_teams/25_time_travel/02_fork_run.py) | Team variant. Member runs from the source team stay attached to the source via `parent_run_id`; the forked team may delegate fresh. | | [Continue from a boundary](https://github.com/agno-agi/agno/blob/main/cookbook/03_teams/25_time_travel/01_continue_from.py) | Team variant of the four-form dispatch demo. | ## Next Steps | Task | Guide | | ----------------------------------------------- | ----------------------------------------------- | | Get valid boundaries from the timeline endpoint | [API Reference](/run-control/api-reference) | | Redo only the last response | [Regenerate](/run-control/regenerate) | | Whole-session clone | [Branch a Session](/run-control/branch-session) |