Session Open/close Behaviors

What are Session Open/close Behaviors?

Session open/close behaviors are the recurring shifts in volatility and order flow around the boundaries of the major trading sessions. Opens concentrate activity: when London or New York comes online, orders accumulated overnight execute, local participants arrive, and ranges tend to expand. Closes bring position squaring and, in FX, benchmark activity around the 4pm London WM/Refinitiv fix, which can produce quick moves into the fix that sometimes partially retrace afterward.

None of this is mechanical: an open can drift and a close can be quiet. The concept is that liquidity and volatility change character at these times, so a strategy tuned to one regime may not survive the other. This is the reasoning behind open-anchored tactics like the opening range and time-boxed frameworks like killzones.

How traders use it

• Timing entries to volatility windows: breakout and momentum tactics are commonly restricted to the London or New York open, when expansion is most likely, rather than run all day.
• Managing around closes: flattening positions or tightening stops into the London fix or the equity close to sidestep erratic fills from squaring and benchmark flows.
• Gating automated systems: session filters that enable a strategy only during the opens or closes it was tested on, keeping it out of liquidity regimes it never saw in development.