DECSET 2026 — Synchronized output

CSI ? 2026 h begins a synchronized update: the terminal buffers all output and does not repaint until CSI ? 2026 l ends the batch, eliminating tearing/flicker when redrawing a frame. A de-facto standard introduced by the terminal-wg / Contour effort and adopted by several terminals.

aka: synchronized output · synchronized update · DECSET 2026 · ?2026h / ?2026l · BSU · ESU · tear-free

frame

DEC-private-mode introducer: \x1b[? ESC [ ? (0x1B 0x5B 0x3F)

terminator (none): ST · BEL

parameters / subcommands

id	name	bytes (ST)	meaning
set	Enable (DECSET)	\x1b[?2026h	CSI ? 2026 h begins a synchronized update (BSU): the terminal stops repainting and buffers subsequent output until the batch ends.
reset	Disable (DECRST)	\x1b[?2026l	CSI ? 2026 l ends the synchronized update (ESU): the terminal atomically renders the buffered frame, avoiding flicker/tearing.

support matrix

terminal	level	since	notes
Contour	full	spec author	Originated/authored the synchronized-output spec.
kitty	full	documented	Implements mode 2026 synchronized updates.
WezTerm	full	documented	Implements mode 2026.
iTerm2	full	3.5+	Supports synchronized output.
Ghostty	full	1.0	Supports mode 2026.

gotchas

You MUST end every begin: an unmatched ?2026h leaves the terminal in a buffering state. Implementations cap the buffer with a timeout, but relying on that causes visible stalls.
Synchronized output prevents TEARING during full-screen redraws (e.g. TUIs, editors); wrap each frame in ?2026h ... ?2026l.
Terminals that don't support 2026 ignore it harmlessly, so it is safe to emit unconditionally — but you can also query support via DECRQM (CSI ? 2026 $ p).
Nesting is generally not supported; treat begin/end as a single non-reentrant batch.
Over tmux/ssh the mode needs passthrough to reach the outer terminal that actually renders.

provenance

source: https://contour-terminal.org/vt-extensions/synchronized-output/
version: Contour synchronized-output spec + terminal-wg mode-2026 documentation, retrieved 2026-05-29
retrieved: 2026-05-29 · updated: 2026-05-29T00:00:00Z

per-fact attribution: