GitHub Copilot SDK Deep Dive: Session Memory

The GitHub Copilot SDK just shipped a new feature: optional memory configuration on session create and resume. Here is what it does, and how it is different from persisted sessions.

The wrong mental model first

When I heared "session memory" my first thought was "persisted sessions" — the ResumeSessionAsync flow that lets you reload an existing session by ID and continue where you left off. That is not what this is. Persisted sessions are about durability of the conversation itself: close the app, reopen it, pick up the thread. Memory configuration is something different.

What memory configuration actually does

Memory is a feature of the Copilot runtime that lets the agent read and write facts across turns — a kind of long-running knowledge store that the agent can consult and update during a session. Think of it as the agent's notepad, not the conversation log.

The new MemoryConfiguration type exposes a single Enabled flag today. You opt in per session, on both create and resume:

var session = await client.CreateSessionAsync(new SessionConfig
{
    Model = "gpt-4o",
    Memory = new MemoryConfiguration { Enabled = true }
});

That's it. The SDK serialises it as { "memory": { "enabled": true } } on the wire. When you leave Memory unset, the field is omitted entirely and the runtime applies its own default.

Now we can ask our agent to remember stuff:

The mode-based default matters

There is a subtle default you need to understand. The SDK has two client modes:

• CopilotClientMode.CopilotCli (the default): Memory is left unset. The runtime decides.
• CopilotClientMode.Empty: Memory defaults to disabled unless you explicitly set it.

A caller-supplied value always wins in either mode. If you are building an app on Empty mode and you want memory, you must opt in explicitly. The runtime will not silently enable it for you.

Persisted sessions vs. memory: the actual difference

	Persisted sessions	Memory configuration
What it stores	The full conversation thread	Facts/notes the agent writes
Lifetime	Until you delete the session	Managed by the runtime
API surface	ResumeSessionAsync(sessionId)	SessionConfig.Memory
Scope	Cross-process, cross-restart	Within the session, agent-controlled

A persisted session lets you reload the conversation. Memory lets the agent remember things across turns within — and potentially across — sessions, depending on how the runtime implements it.

You can use both at the same time: resume a persisted session with memory enabled, and the agent brings its notepad along.

Resuming with memory

ResumeSessionAsync also accepts the memory configuration:

var session = await client.ResumeSessionAsync(sessionId, new ResumeSessionConfig
{
    Memory = new MemoryConfiguration { Enabled = true }
});

This means you can control memory independently of whether the session is new or resumed. Useful if you want to enable memory for an existing session that was originally created without it.

More information

PR #1617 — SDK: add optional memory configuration to session create and resume

GitHub Copilot SDK Deep Dive: CopilotClientMode