When do Rogues learn Sinister Strike?

Rank 1 at level 1, with later ranks at 6, 14, 22, 30, 38, 46, 54. Visit a class trainer in any capital.

Did Sinister Strike change from Classic?

No recorded differences from Classic 1.12 in this snapshot.

Rank	Level	Cost / range / cast	Effect	Classic 1.12
Rank 1	1	45 Energy · Melee Range · Instant	An instant strike that causes 3 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 2	6	45 Energy · Melee Range · Instant	An instant strike that causes 6 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 3	14	45 Energy · Melee Range · Instant	An instant strike that causes 10 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 4	22	45 Energy · Melee Range · Instant	An instant strike that causes 15 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 5	30	45 Energy · Melee Range · Instant	An instant strike that causes 22 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 6	38	45 Energy · Melee Range · Instant	An instant strike that causes 33 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 7	46	45 Energy · Melee Range · Instant	An instant strike that causes 52 damage in addition to your normal weapon damage. Awards 1 combo point.	same
Rank 8	54	45 Energy · Melee Range · Instant	An instant strike that causes 68 damage in addition to your normal weapon damage. Awards 1 combo point.	same

Remorseless Attacks (Assassination row 1): After killing a non-trivial enemy, gives you a 40% increased critical strike chance on your next Sinister Strike, Backstab, Ambush, Mutilate, or Ghostly Strike. Lasts 20 sec.
Lethality (Assassination row 3): Grants 20% increased Critical Strike damage to your Sinister Strike, Gouge, Backstab, Mutilate, Ghostly Strike, and Hemorrhage abilities.
Cold Blood (Assassination row 4): When activated, increases the critical strike chance of your next Sinister Strike, Backstab, Ambush, Eviscerate, or Mutilate by 100%.
Efficient Strikes (Combat row 1): Reduces the Energy costs of Sinister Strike and Hemorrhage by 5.
Aggression (Combat row 4): Increases the damage of Sinister Strike and Eviscerate by 15%.

Source: beta client 1.60.1.70753. Spell ID 11294.