Diff a forked Session against its source

curl --request GET \
  --url https://api.checkfu.com/v1/sessions/{id}/diff \
  --header 'Authorization: Bearer <token>' \
  --header 'checkfu-version: <checkfu-version>'

import requests

url = "https://api.checkfu.com/v1/sessions/{id}/diff"

headers = {
    "checkfu-version": "<checkfu-version>",
    "Authorization": "Bearer <token>"
}

response = requests.get(url, headers=headers)

print(response.text)

const options = {
  method: 'GET',
  headers: {'checkfu-version': '<checkfu-version>', Authorization: 'Bearer <token>'}
};

fetch('https://api.checkfu.com/v1/sessions/{id}/diff', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.checkfu.com/v1/sessions/{id}/diff",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "GET",
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "checkfu-version: <checkfu-version>"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.checkfu.com/v1/sessions/{id}/diff"

	req, _ := http.NewRequest("GET", url, nil)

	req.Header.Add("checkfu-version", "<checkfu-version>")
	req.Header.Add("Authorization", "Bearer <token>")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.get("https://api.checkfu.com/v1/sessions/{id}/diff")
  .header("checkfu-version", "<checkfu-version>")
  .header("Authorization", "Bearer <token>")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.checkfu.com/v1/sessions/{id}/diff")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Get.new(url)
request["checkfu-version"] = '<checkfu-version>'
request["Authorization"] = 'Bearer <token>'

response = http.request(request)
puts response.read_body

{
  "source": "<string>",
  "branch": "<string>",
  "through_event": "<string>",
  "through_sequence": 1,
  "source_tail": {
    "session": "<string>",
    "positions": 1,
    "events": 1,
    "unavailable": 1,
    "by_type": [
      {
        "type": "<string>",
        "count": 1
      }
    ],
    "settled": {
      "type": "<string>",
      "seq": 1
    },
    "last_seq": 1,
    "complete": true
  },
  "branch_tail": {
    "session": "<string>",
    "positions": 1,
    "events": 1,
    "unavailable": 1,
    "by_type": [
      {
        "type": "<string>",
        "count": 1
      }
    ],
    "settled": {
      "type": "<string>",
      "seq": 1
    },
    "last_seq": 1,
    "complete": true
  },
  "projection": {
    "source_status": "<string>",
    "branch_status": "<string>",
    "diverged_fields": [
      "<string>"
    ]
  },
  "source_outcome": {
    "outcome": "<string>",
    "iteration": 1,
    "result": "<string>"
  },
  "branch_outcome": {
    "outcome": "<string>",
    "iteration": 1,
    "result": "<string>"
  },
  "source_context": {
    "cumulative_tokens": 1,
    "current_context_tokens": 1,
    "condensations": 1
  },
  "branch_context": {
    "cumulative_tokens": 1,
    "current_context_tokens": 1,
    "condensations": 1
  },
  "wire": {
    "canonical_form_version": 1,
    "source_calls": 1,
    "branch_calls": 1,
    "compared": 1,
    "matched": 1,
    "unreadable": 1,
    "truncated": true,
    "first_divergence": {
      "index": 1,
      "source_seq": 123,
      "branch_seq": 123
    }
  }
}

{
  "error": {
    "type": "validation.malformed",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#validation-malformed"
  }
}

{
  "error": {
    "type": "auth.invalid_key",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#auth-invalid-key"
  }
}

{
  "error": {
    "type": "auth.disabled_tenancy",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#auth-disabled-tenancy"
  }
}

{
  "error": {
    "type": "validation.not_found",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#validation-not-found"
  }
}

{
  "error": {
    "type": "budget.exceeded",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#budget-exceeded"
  }
}

{
  "error": {
    "type": "runtime.internal",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#runtime-internal"
  }
}

Diff a forked Session against its source

Compares a fork with its recorded source: id must be a fork, and lineage is read from the branch’s own ledger rather than from anything the caller claims. Returns the fork boundary (through_event, through_sequence), a tail summary per side past that boundary (positions scanned, event counts by type, the settling event, last_seq, and a complete flag that goes false when the bounded scan truncated), the diverged projection fields and both statuses, plus each side’s Outcome and context-token totals. Unavailable positions are counted rather than guessed at, so erasure stays as visible here as in an export, and the whole view is derived on every read. An admin or root key may add wire=true for the model-wire drift block.

Checkfu support posture: alpha; hosted. Required evidence journey: session-turn. Deployment-specific readiness and the latest proven release are available from GET /v1/support/capabilities.

GET

sessions

{id}

diff

Diff a forked Session against its source

curl --request GET \
  --url https://api.checkfu.com/v1/sessions/{id}/diff \
  --header 'Authorization: Bearer <token>' \
  --header 'checkfu-version: <checkfu-version>'

import requests

url = "https://api.checkfu.com/v1/sessions/{id}/diff"

headers = {
    "checkfu-version": "<checkfu-version>",
    "Authorization": "Bearer <token>"
}

response = requests.get(url, headers=headers)

print(response.text)

const options = {
  method: 'GET',
  headers: {'checkfu-version': '<checkfu-version>', Authorization: 'Bearer <token>'}
};

fetch('https://api.checkfu.com/v1/sessions/{id}/diff', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.checkfu.com/v1/sessions/{id}/diff",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "GET",
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "checkfu-version: <checkfu-version>"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"net/http"
	"io"
)

func main() {

	url := "https://api.checkfu.com/v1/sessions/{id}/diff"

	req, _ := http.NewRequest("GET", url, nil)

	req.Header.Add("checkfu-version", "<checkfu-version>")
	req.Header.Add("Authorization", "Bearer <token>")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.get("https://api.checkfu.com/v1/sessions/{id}/diff")
  .header("checkfu-version", "<checkfu-version>")
  .header("Authorization", "Bearer <token>")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.checkfu.com/v1/sessions/{id}/diff")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Get.new(url)
request["checkfu-version"] = '<checkfu-version>'
request["Authorization"] = 'Bearer <token>'

response = http.request(request)
puts response.read_body

{
  "source": "<string>",
  "branch": "<string>",
  "through_event": "<string>",
  "through_sequence": 1,
  "source_tail": {
    "session": "<string>",
    "positions": 1,
    "events": 1,
    "unavailable": 1,
    "by_type": [
      {
        "type": "<string>",
        "count": 1
      }
    ],
    "settled": {
      "type": "<string>",
      "seq": 1
    },
    "last_seq": 1,
    "complete": true
  },
  "branch_tail": {
    "session": "<string>",
    "positions": 1,
    "events": 1,
    "unavailable": 1,
    "by_type": [
      {
        "type": "<string>",
        "count": 1
      }
    ],
    "settled": {
      "type": "<string>",
      "seq": 1
    },
    "last_seq": 1,
    "complete": true
  },
  "projection": {
    "source_status": "<string>",
    "branch_status": "<string>",
    "diverged_fields": [
      "<string>"
    ]
  },
  "source_outcome": {
    "outcome": "<string>",
    "iteration": 1,
    "result": "<string>"
  },
  "branch_outcome": {
    "outcome": "<string>",
    "iteration": 1,
    "result": "<string>"
  },
  "source_context": {
    "cumulative_tokens": 1,
    "current_context_tokens": 1,
    "condensations": 1
  },
  "branch_context": {
    "cumulative_tokens": 1,
    "current_context_tokens": 1,
    "condensations": 1
  },
  "wire": {
    "canonical_form_version": 1,
    "source_calls": 1,
    "branch_calls": 1,
    "compared": 1,
    "matched": 1,
    "unreadable": 1,
    "truncated": true,
    "first_divergence": {
      "index": 1,
      "source_seq": 123,
      "branch_seq": 123
    }
  }
}

{
  "error": {
    "type": "validation.malformed",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#validation-malformed"
  }
}

{
  "error": {
    "type": "auth.invalid_key",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#auth-invalid-key"
  }
}

{
  "error": {
    "type": "auth.disabled_tenancy",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#auth-disabled-tenancy"
  }
}

{
  "error": {
    "type": "validation.not_found",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#validation-not-found"
  }
}

{
  "error": {
    "type": "budget.exceeded",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#budget-exceeded"
  }
}

{
  "error": {
    "type": "runtime.internal",
    "message": "<string>",
    "more": "https://docs.checkfu.com/reference/errors#runtime-internal"
  }
}

Authorizations

Authorization

string

header

required

Bearer authentication header of the form Bearer <token>, where <token> is your auth token.

Headers

checkfu-version

enum<string>

required

Available options:

2026-08-24

Path Parameters

string

required

Pattern: ^sess_[0-9a-f]{32}$

Query Parameters

wire

enum<string>

Available options:

true

Response

Success

source

string

required

Pattern: ^sess_[0-9a-f]{32}$

branch

string

required

Pattern: ^sess_[0-9a-f]{32}$

through_event

string

required

Pattern: ^evt_[0-9a-f]{32}$

through_sequence

integer

required

Required range: x > 0

source_tail

object

required

Show child attributes

branch_tail

object

required

Show child attributes

projection

object

required

Show child attributes

source_outcome

object | null

required

Show child attributes

branch_outcome

object | null

required

Show child attributes

source_context

object | null

required

Show child attributes

branch_context

object | null

required

Show child attributes

wire

object

Show child attributes

Developer tools

Canonical tables

Author protocols

Generated HTTP API

Diff a forked Session against its source

Authorizations

Headers

Path Parameters

Query Parameters

Response