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[Bug]: History Length = 0, is returning all the history #573
Description
What happened?
As per the spec defined in website, historyLength=0 should not return any history. But we are getting all the history.
https://a2a-protocol.org/latest/specification/#323-stream-response
Relevant log output
curl -s -X POST "http://localhost:9000/" -H "Content-Type: application/json" -d '{
"jsonrpc": "2.0",
"method": "message/send",
"params": {
"message": {
"messageId": "your-unique-message-id",
"role": "user",
"parts": [
{"text": "What is 2+3 ?"}
]
},
"configuration": {
"acceptedOutputModes": ["text/plain"],
"historyLength":1
}
}'
{
"id": 1,
"jsonrpc": "2.0",
"result": {
"artifacts": [
{
"artifactId": "a67dace3-cd78-413e-badc-e0cf94507d18",
"name": "agent_response",
"parts": [
{
"kind": "text",
"text": "### Simple Math\n\n2 + 3 = **5**\n\nIf you have any questions about your finances, spending habits, budgeting, or would like to explore your account, I'm here to help!\n"
}
]
}
],
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"history": [
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "your-unique-message-id",
"parts": [
{
"kind": "text",
"text": "What is 2+3 ?"
}
],
"role": "user",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "379b0031-cf8f-4354-93ea-f28a25e88f3c",
"parts": [
{
"kind": "text",
"text": "###"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "5ca7940e-36a1-4bea-bf02-3d2bdd1ca424",
"parts": [
{
"kind": "text",
"text": " Simple Math\n\n2 + 3"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "9d6739a1-95e5-4dc2-93c2-71a4f77fefc8",
"parts": [
{
"kind": "text",
"text": " = **5**\n\nIf"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "7865ceab-3c21-4f2c-bf56-7f3ed8054156",
"parts": [
{
"kind": "text",
"text": " you have"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "07e69ddb-c745-4ad7-8550-d7f6f4f2676e",
"parts": [
{
"kind": "text",
"text": " any questions about your finances,"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "e8e474b0-2c7d-4d73-a397-aa93f915c9ad",
"parts": [
{
"kind": "text",
"text": " spending"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "4ac5f332-5512-4b14-8e78-4bfaa29e2d5b",
"parts": [
{
"kind": "text",
"text": " habits"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "fcefe6a4-a50a-4b05-9dfd-8b65af250961",
"parts": [
{
"kind": "text",
"text": ", bu"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "55a6d3e0-9e10-49b9-91bb-480a56e319c4",
"parts": [
{
"kind": "text",
"text": "dgeting, or woul"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "49259de3-c2f9-4f5c-80d1-275fd3143d63",
"parts": [
{
"kind": "text",
"text": "d like to explore"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "258f271e-5833-481c-a269-3f17a54c426b",
"parts": [
{
"kind": "text",
"text": " your"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "ee6eff49-0c9b-4165-8473-a3379c3ae6ee",
"parts": [
{
"kind": "text",
"text": " account, I'm here to"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
},
{
"contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
"kind": "message",
"messageId": "83b174b4-b2ec-4e5a-ad0b-46e9b796c3c4",
"parts": [
{
"kind": "text",
"text": " help!"
}
],
"role": "agent",
"taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
}
],
"id": "07f2a3b2-f498-438f-87b4-6"
}
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Activity
lkawka commentedon Dec 1, 2025
Hi Anand,
You're right, the SDK should behave differently.
The root cause is that the specification was recently updated, and our current implementation has not yet integrated these changes. Specifically, there is an issue with differentiating between unset values and explicit 0 values in the current SDK version.
The latest specification addresses this by making the
history_lengthfield optional. We’re currently planning how to deal with the recent specification changes in the SDK and will then address this issue.anandsugumaran commentedon Dec 2, 2025
Hi @lkawka
Thanks for confirming. Will wait for this change in upcoming releases.
fix: historyLength=0 returns full history (a2aproject#573)
fix: historyLength=0 returns full history (a2aproject#573)
fix: properly handle unset and zero history length
fix: properly handle unset and zero history length
fix: properly handle unset and zero history length (#717)
ishymko commentedon Feb 23, 2026
This was fixed for 1.0 release via #717.